There has recently been an accelerated trend toward the replacement of displays on mobile phones by those of touch panel type. Unfortunately, the display of touch panel type has the disadvantage of becoming easily soiled with sebum etc. because it is usually bare and subject to direct contact with the fingers and cheeks of the user. Thus there is a growing demand for technologies to protect the display from soiling with fingerprints and to make the display easily cleanable, thereby improving appearance and visibility. This demand is fulfilled by any conventional water- and oil-repellent that forms an easy-to-clean film having good water- and oil-repellency. Such a conventional product, however, has the disadvantage of greatly varying in durability from one batch of film to another. Moreover, it involves difficulties in forming a smooth film due to agglomeration of particles therein. This has stimulated the development of a new surface treating agent and a method of invariably forming a high-performance coating film.
In the meantime, any compound containing fluorooxyalkylene groups generally exhibits water- and oil-repellency, chemical resistance, lubricity, releasability, and stain resistance on account of its very low surface free energy. Thanks to these properties, it finds a variety of industrial uses as water- and oil-repellent stain-resistant agents for paper and fiber, slip agents for magnetic recording media, oil protectants for precision machines, mold release agents, cosmetics, and protective film. On the other hand, the aforesaid properties imply nonadherence to substrates, and hence the aforesaid compound can be applied to the substrate surface but the resulting coating film does not firmly adhere to the substrate surface.
By the way, among well-known agents to bind an organic compound to a substrate such as glass and cloth are silane coupling agents, which are in general use for coating on the surface of various substrates. Any silane coupling agent has organic functional groups and reactive silyl groups (usually alkoxysilyl groups) in one molecule. The alkoxysilyl groups undergo the self-condensation reaction induced by moisture in air, thereby forming a coating film. This coating film is durable and strong because of the chemical and physical bonding of alkoxysilyl groups to the surface of glass or metal.
One example of the coupling agents having the alkoxysilyl groups as mentioned above is disclosed in Patent Document 1 (JP-A 2003-238577). It is a silane modified with a polymer containing linear perfluorooxyalkylene groups represented by the formula below. This silane is used for surface treatment of glass and antireflective film. The treated glass or film is superior in slipperiness, releasability, and wear resistance, but lacks stable high-performance properties. The lack of durability is due to the presence of non-fluorine groups on the molecular terminals, the non-fluorine groups being liable to agglomeration during or after the coating process.
wherein Rf is a divalent linear perfluorooxyalkylene group; R is an alkyl group or a phenyl group having 1 to 4 carbon atoms; X is a hydrolyzable group; n is an integer of 0 to 2; m is an integer of 1 to 5; and a is 2 or 3.